Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically cross-linked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically cross-linked elastomers, may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of this patent are readily useable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear or garden hose by an extrusion process as are the improved compositions of the present invention, wherein both improved physical and rheological properties are realized.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically cross-linked sulfonated elastomers prepared by this process do not exhibit both the improved physical and rheological properties as well as improved weathering stability and compression set properties of the compositions of the present invention.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by this process are not as suitable for the manufacture of high performance elastomeric articles such as footwear formed by an injection molding process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, herein incorporated by reference, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer. Again, the compositions of the present invention are more adaptable for use in the manufacture of high performance elastomeric articles.
Products resulting from the aforementioned methods for obtaining neutralized sulfonated elastomeric compositions, possess either unsuitable rheological or physical properties as well as inferior weathering stability and compression set for the applications envisioned in the present invention.
For example, the physical properties of these resultant sulfonated elastomeric products of these aforementioned patents are unsuitable for a major application of an injection molding process, namely the manufacture of footwear, or the manufacture of garden hose by an extrusion process wherein excellent resilience, dimensional stability, good compression set, excellent low and high temperature flexibility, excellent weathering stability, excellent flex fatigue, and good abrasion are needed. Furthermore, the high melt viscosity and melt elasticity of these materials makes injection molding difficult if not impossible. These materials of the aforementioned patents which are generally processable by only compression molding have marginally satisfactory physical properties, compression set and weathering stability for these major applications of footwear and garden hose. The present invention provides improvements over those materials.
The materials cost of the compositions of the instant invention is substantially reduced over those of the aforementioned patents, wherein these previous patents failed to realize the criticality of the proper selection of the chemical and physical uniqueness of the basic elastomeric backbone, the degree of sulfonation, the proper selection of neutralizing agent in conjunction with plasticization, and the critical selection of an extenders ability to extend these sulfonated polymers with a mixture of a nonpolar process oil and inorganic filler and carbon black. Unsulfonated elastomers, when extended with oils and fillers, show a general deterioration in physical and rheological properties as well as weathering stability as is clearly shown in the Detailed Description of the present invention. Quite surprisingly, through the proper selection of nonpolar process oil, inorganic filler and carbon black within a critical ratio of filler to oil, the sulfonated elastomeric composition of the present invention shows a marked improvement in both rheological and physical properties as well as compression set properties and weathering stability.
The use of ultraviolet stabilizers is well known in the elastomeric and polymeric art fields. However, the use of ultraviolet stabilizers in the preparation of sulfonated elastomeric blend compositions for extrusion and injection molding compositions results in a general significant deterioration of physical properties due to the excessively large amounts of stabilizer needed in order to obtain suitable weathering stability with the instant sulfonated elastomers.
Compression set is a second significant drawback of nearly all sulfonated elastomer based thermoplastic elastomer compounds. For most rubbery applications compression set values at room temperature of about 20 to 30% would be desirable for this would suggest a good recovery from a long term deformation. Sulfo EPDM compounds generally possess compression set values on the order of 50% .+-. 10%. The incorporation of a UV stabilizer can further exacerbate the set behavior of these systems to an extent that values of 60 to 70% are achieved. This is unacceptable for many applications.
The unique and novel improved compositions of the present invention overcome the deficiencies of the aforementioned U.S. patents and applications from both a rheological and physical properties aspect as well as providing excellent compression set properties and improved weathering stability. The blend compositions of the present invention solve the problem of having a material which has both desirable rheological and physical properties for the manufacture of an elastomeric article as an elastomeric footwear or garden hose wherein the extrudate of the resultant compositions do not exhibit early melt fracture during extrusion processing as is the case in some of the aforementioned patents and provides an elastomeric article having both improved compression set properties and weathering stability.